boundaryMesh()[fluid2PatchIndex_].faceCentres() 什么意思

OpenFOAM
1 
void Foam::fluidStructureInterface::calcFluid2ToSolidInterpolator() const
{
    // Find global face zones
    if (fluid2ToSolidPtr_)
    {
        FatalErrorIn
        (
            "void fluidStructureInterface::"
            "calcFluid2ToSolidInterpolator() const"
        )
            << "Fluid2 to solid interpolator already exists"
                << abort(FatalError);
    }

    fluid2ToSolidPtr_ =
        new zoneToZoneInterpolation
        (
            fluidMesh2().faceZones()[fluid2ZoneIndex_](),
            solidMesh().faceZones()[solidZoneIndex_](),
            intersection::VISIBLE
        );


    Info << "Checking fluid2-to-solid interpolator" << endl;
    {
        vectorField fluid2PatchFaceCentres =
            vectorField
            (
                fluidMesh2().boundaryMesh()[fluid2PatchIndex_].faceCentres()
            );

        vectorField fluid2ZoneFaceCentres
        (
            fluidMesh2().faceZones()[fluid2ZoneIndex_].size(),
            vector::zero
        );

        const label fluid2PatchStart =
            fluidMesh2().boundaryMesh()[fluid2PatchIndex_].start();

        forAll (fluid2PatchFaceCentres, i)
        {
            fluid2ZoneFaceCentres
            [
                fluidMesh2().faceZones()[fluid2ZoneIndex_].whichFace
                (
                    fluid2PatchStart + i
                )
            ] =
                fluid2PatchFaceCentres[i];
        }

        // Parallel data exchange: collect faceCentres field on all processors
        reduce(fluid2ZoneFaceCentres, sumOp<vectorField>());

        vectorField solidZoneFaceCentres =
            fluid2ToSolidPtr_->faceInterpolate
            (
                fluid2ZoneFaceCentres
            );

        vectorField solidPatchFaceCentres
        (
            solidMesh().boundaryMesh()[solidPatchIndex_].size(),
            vector::zero
        );

        const label solidPatchStart =
            solidMesh().boundaryMesh()[solidPatchIndex_].start();

        forAll(solidPatchFaceCentres, i)
        {
            solidPatchFaceCentres[i] =
                solidZoneFaceCentres
                [
                    solidMesh().faceZones()[solidZoneIndex_]
                   .whichFace(solidPatchStart + i)
                ];
        }

        scalar maxDist = gMax
        (
            mag
            (
                solidPatchFaceCentres
              - solidMesh().boundaryMesh()[solidPatchIndex_].faceCentres()
            )
        );

        Info << "Fluid2-to-solid face interpolation error: " << maxDist
            << endl;
    }
}

这是我复制流体一其中的一个私有成员函数，我认为这个函数是有必要加的，
fluidMesh2().boundaryMesh()[fluid2PatchIndex_].faceCentres()，
类似这样的长句有些看不懂

2

fluidMesh2().boundaryMesh()[fluid2PatchIndex_].faceCentres() ，这个意思是在 fluidMesh2 里面找到与 solid 部分耦合的边界 boundaryMesh()[fluid2PatchIndex_]，取其面的中心坐标 faceCentres()。